This invention pertains to electro-optical distance-measuring apparatus, and more particularly, to a unique positional and attitudinal arrangement of components in such apparatus which promotes a high degree of accurate performance over a relatively wide dynamic range of distances.
There are many instances, such as for example in a plywood mill, where it is desired to make an accurate measurement of the distance between a known location and a particular object, so as to locate the object (or more particularly, the object's near surface) as precisely as possible in space. A preferred embodiment of the present invention is described herein in conjunction with a block centering operation, wherein it is important to be able to position a log in a closely controlled position relative to a veneer peeler blade.
According to this preferred embodiment a small-diameter laser beam is projected along one axis toward what might be thought of as a viewing zone, in which logs are expected to appear prior to a block centering operation. "Looking", so-to-speak, along another and intersecting axis is an optically sensitive viewer which looks for light from this beam which is reflected from a log's surface.
It is known, and expected, that logs appearing within this zone will have different diameters. For example, it might be typical to expect logs having diameters in the range of about 8-inches to about 48-inches. Obviously, the distance-measuring system of the invention must be capable of monitoring logs within such diameter range. As will be more fully explained below, the angle between the beam-projection axis and the viewing axis is selected both to accommodate the "dynamic range" of expected log-diameter differences, and to maximize the resolution accuracy of viewed reflected light, so that such accuracy does not vary, in any appreciable sense, over the entire selected dynamic range.
Employed in the "viewing" portion of the apparatus are a lens and a linear (straight-line) photodetector array. When the laser beam strikes the surface of a log, the lens focuses onto the array an image of the reflected light. The position of such image, along the length of the array, is directly interpretable to indicate the distance to the impinged log surface. Throughout the dynamic range of the apparatus, and as logs of different diameters are observed, imaged reflected light will strike the photodetector array at different specific points along its length.
A unique and important feature of the present invention is the discovery that the angular positioning of the photodetector array is critical to assuring that, throughout the dynamic range which is contemplated, a reflected image on the array will always be in sharp focus thereon. In other words, with proper attention to such angular positioning, the focus of the image is independent of log-surface distance. If attention is not paid to this important angular positioning of the array, the focus of a reflected image thereon will change throughout the dynamic range, and will thus cause significant resolution accuracy differences.
These and various other objects and advantages which are attained by the invention will become more fully apparent as the description which now follows is read in conjunction with the accompanying drawing.